Shift of millet rhizosphere bacterial community during the maturation of parent soil revealed by 16S rDNA high-throughput sequencing

Microorganisms, particularly bacteria, are important components of mature soil capable of high crop yields. However, changes in the diversity and abundance of bacteria during the maturation of parent soil have not been thoroughly elucidated to date. In this study, we determined the diversity of the bacterial community in millet rhizospheres from mellow soil (MS), immature soil (IS), and a mixture of MS and IS (MS-IS mixture) using high-throughput Illumina sequencing. We also analysed soil chemical properties, microbial carbon, microbial nitrogen and enzyme activities, and we correlated them with bacterial taxa. In different rhizosphere soil samples, higher bacterial diversity was found in MS than in IS or the MS-IS mixture. The same trends were observed for soil organic carbon (SOC), available nitrogen (AN), available phosphorus (AP), carbon to nitrogen ratio (C/N), soil microbial carbon, soil microbial nitrogen and soil enzyme activities. Compared to IS, MS harboured a higher abundance of two phyla (Proteobacteria and Actinobacteria) but a lower abundance of five phyla (Chloroflexi, Acidobacteria, Bacteroidetes, Nitrospirae and Firmicutes) and a higher abundance of 22 genera but a lower abundance of 13 genera. A redundancy analysis indicated that the higher abundance of seven genera (Caenimonas, Gemmatimonas, Lysobacter, Ramlibacter, Devosia, Mycobacterium and Streptomyces) was correlated with higher levels of SOC, AN and C/N. Phosphatase, invertase and urease were correlated with higher levels of SOC, AN and C/N. These findings suggest that higher abundance of some specific bacteria accelerates soil maturation by increasing soil chemical properties and soil enzyme activities, thereby leading to higher crop yields.